The Jamaica international came off with 20 minutes left of the Scottish Premier League opener at Dingwall, which ended in stalemate.
Motherwell travel to Athens for Wednesday's third qualifying round second leg 2-0 down, and again lacked a cutting edge today as they were held by a solid County side, who stretched their unbeaten league run to 35 games.
"Humphrey came off with a bit of a hamstring problem," Motherwell manager Stuart McCall said.
"He hasn't pulled it but he will be a doubt for Athens."
Omar Daley started on the opposite flank to Humphrey and could be in line to feature in the Olympic Stadium, with Motherwell lacking creativity in the final third at the Global Energy Stadium despite dominating possession.
Michael Higdon headed over from close range just before the break but County otherwise restricted their opponents and occasionally threatened with set-pieces themselves.
Manager Derek Adams declared himself "delighted" with the point on their SPL debut.
"I thought we coped with Motherwell very well, a team that came off a Champions League game with Panathinaikos," he added.
"They are quick on the wings and direct. I'm delighted to keep our 35-game unbeaten run going. We are happy.
"Motherwell started well and kept good possession. They didn't open us up and that was important.
"It was a difficult occasion for us, our first game in the SPL, but we coped well and we are delighted to get the day over and done with and a point on the board."
McCall was far less pleased after his side failed to trouble former Fir Park goalkeeper Michael Fraser.
"I was disappointed with the fact that we didn't make more use of the ball that we had," McCall said.
"We dominated the possession for a long time and we didn't make any real clear-cut chances.
"They defended solidly but we can play better. We've got to take the positives, a clean sheet and the first point on the board.
"It was obviously going to be a tough first game against a newly-promoted side but I'm slightly disappointed in our own performance when we had the ball.
"But we'll settle for a point because neither side deserved to win or lose."
